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Homework Help: Collisions and Change in Momentum

  1. Feb 26, 2009 #1
    1. The problem statement, all variables and given/known data

    A ball of mass 4.7 kg moving with speed of 1.9 m/s in the x-direction hits a wall and bounces back with the same speed in the -x-direction. What is the change of momentum of the ball? And in what direction?

    2. Relevant equations

    p=mv

    3. The attempt at a solution

    P=mv
    P=4.7*1.9
    P=8.93
     
  2. jcsd
  3. Feb 26, 2009 #2

    LowlyPion

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    So what is the initial momentum?

    What is the final momentum?

    What is the difference?
     
  4. Feb 26, 2009 #3
    The initial is 8.93 and the final is -8.93..so total momentum is 0? In what direction?
     
  5. Feb 26, 2009 #4
    Try again using pf - pi to find the difference.
     
  6. Feb 26, 2009 #5

    LowlyPion

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    Sorry, signs matter.

    Initial momentum = P
    Final momentum = -P

    Final - initial = Δ = (-P) - P = -2P

    Negative because Δx/Δt is toward -x.
     
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